This relates to a memory including bipolar junction transistor select devices.
Phase change memories are formed by memory cells connected at the intersections of bitlines and wordlines and comprising each a memory element and a selection element.
Each memory element comprises a phase change region made of a phase change material, i.e., a material that may be electrically switched between a generally amorphous and a generally crystalline state across the entire spectrum between completely amorphous and completely crystalline states. Typical materials suitable for such an application include various chalcogenide elements. The state of the phase change materials is non-volatile, absent application of excess temperatures, such as those in excess of 150° C. for extended times. When the memory is set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reprogrammed, even if power is removed. This is because the programmed value represents a phase or physical state of the material (e.g., crystalline or amorphous).
Select devices, access devices, or select elements may be formed according to different technologies, for example they can be implemented by diodes, by MOS transistors or bipolar transistors.
The collector region of a bipolar select device is formed by a buried, shared region of the substrate, overlaid by a shared base region. An emitter region and a base contact region are formed in the base region for each memory cell. Each emitter region is then connected to an own memory element, in turn connected to a bitline. The base contact is connected to a wordline through plugs extending in an insulating layer overlying the substrate. The memory cells that are adjacent in the direction of the rows of the memory array are connected to a same wordline. The memory cells that are adjacent in the direction of the columns of the memory array are connected to a same bitline.